1. Field of the Invention
The present invention relates to demountable connectors of electric circuits of printed circuit boards, and in particular, to a zero insertion force electrical connector.
The invention may be used for electrical connection within a unit or between units in electronic equipment using printed circuit boards and switching devices.
2. Description of the Prior Art
In widely-known zero insertion force electrical connectors using cam mechanisms, worm gears, sliding bar mechanisms, the force required to open contacts by some mechanism is a factor which limits the permissible number of contact positions. Designing zero insertion force electrical connectors is complicated by eventual warping, scatter of tolerances and out-of-planeness of the circuit boards being connected. Furthermore, known connectors have mechanisms for opening contacts of complicated design, the manufacture thereof is complicated, and they have low reliability in operation.
Known in the art is a zero insertion force electrical connector (GB, B, No. 1542889) comprising a support supporting an insulator housing and a row of contacts, a cam bar extending along the contacts, a drive mechanism for longitudinally shifting the bar, a cooperating means which provides engagement between the cam bar and support during longitudinal movement on the bar and which diagonally moves the bar away from the support to spread the contacts. The contacts are closed upon reversing rotation of the drive mechanism.
Simultaneous opening and closure of all contacts results in an increased mechanical load on the drive mechanism which limits the number of contacts used in the connector, causes intensive wear of the drive mechanism and makes the connector design more complicated.
Known in the art is a zero insertion force electrical connector (DE, B, No. 2707122) comprising an insulator housing having recesses in which elastic contacts are mounted and a U-shaped longitudinal slot for receiving a bar which compresses the contacts and which forms a means for closing the contacts. Another embodiment of this connector comprises vertically movable cams mounted opposite to each pair of contacts and driven by a bar or slider.
According to a first embodiment of the connector, contacts are closed due to a movement of the bar which compresses them. This results in a gradual increase in a force produced by closure of the entire group of contacts. Shifting the cams which compress the contacts by means of the bar or slider makes it possible to reduce the force produced by closure of contacts. But a second embodiment of the connector is of a complex design. Furthermore, mechanical stresses produced in the contacts are at maximum when the contacts are closed, which results in a residual deformation of the connector contacts causing a poor connection with a member being switched during operation.
Known in the art is a zero insertion force electrical connector (U.S. Pat. No. 4,275,944) comprising an insulator housing having a longitudinal slot in a top wall thereof for receiving a mating member. Secured in a lower wall of the housing are elastic contacts placed in side walls of the housing. The housing also has a longitudinal passageway for reciprocations of a key therein for opening and closing elastic contacts. The key is made in the form of a rod having a constant cross-sectional area of its working portion.
Each contact has bowed arms engageable with a member being switched and projections for mounting the contacts in the recesses. Placed between the contact arms along the connector are flexible inserts which define the passageway for movement of the key therein.
Despite of the fact that the friction force of the key decreases during opening of the contact arms due to the provision of inserts disposed between the key and inner end faces of the contact arms, the insertion force of the key increases with an increase in the number of open contacts which limits the admissible number of contacts in the connector.